The present invention relates to a sheet feeding apparatus for picking sheets one by one from a stack of sheets, and moving the picked sheets away from the stack.
Sheet feeding apparatus of this kind are commonly of either the vacuum pick or friction pick type. Vacuum pick systems use a suction member to separate the first sheet from the rest of the stack and are particularly suitable for handling sheets which are nonporous, such as currency notes in an automated teller machine (ATM). Friction type pick systems are also commonly used in ATMs. Some friction pick systems are advantageous in that they have higher feed rate capabilities than vacuum type systems and are of relatively simple construction. In addition to picking currency notes, sheet feeding apparatus of the vacuum pick or friction pick type may be used for picking other types of sheets from a stack, such as photocopier sheets, tickets, vouchers, sheets of stamps, travelers cheques etc.
Friction pick systems commonly use a rotating pick roller having a high friction material disposed over its entire outer peripheral surface or over a localized area thereof. When the pick roller makes contact with a first sheet of a stack, the frictional force exerted on the sheet is greater than the frictional force between this sheet and the next sheet in the stack, which causes the first sheet to be separated from the stack and moved away by the rotating roller. However, the high friction surfaces on the picker roller tend to become worn relatively quickly and need to be replaced. This is inconvenient and expensive, as frequent maintenance of the feeding system is required. Moreover, the reliability of the feeding system is reduced as the friction surface becomes progressively worn.
Rotating friction belts have also been used in friction pick systems to pick sheets from a stack and in general are less susceptible to wear than friction rollers. Since the rotating belt presents a larger friction surface than a pick roller and the portion of the belt which engages the stack is constantly changing, wear of the belt tends to be spread over the length of the belt rather than on a localized area thereof. A known pick apparatus having friction belt means is disclosed in EP-A-0329 296. This known apparatus has a driven belt for delivering sheets from a stack, where the belt is brought into contact with the bottom sheet of a stack of sheets at the commencement of a pick operation and is retracted therefrom when the leading edge of the bottom sheet has been moved into engagement with feed rollers which carry the picked sheet away from the stack. Since the time in which the belt is in contact with the stack of sheets during a picking operation is minimal, such an arrangement is advantageous with respect to wear of the belt. However, the apparatus has the disadvantage that it has a limited feed rate capacity, since the belt is decelerated and brought to rest after each pick operation and therefore is not suitable for many applications. A further disadvantage of this apparatus is that the mechanism used to achieve shifting of the belt is complex, involving cams, levers and lifting bars.